This invention relates to a process for preparing pressure-sensitive adhesive coated substrates having a release layer releasably affixed thereto and, more particularly, to a new method of laminating a continuous web of release paper to a web of paper face stock coated with a water-dispersed pressure-sensitive adhesive.
At present water-dispersed pressure-sensitive adhesive composites (paper face stock, adhesive, release paper) are prepared by (a) applying the water-dispersed pressure-sensitive adhesive to a continuous web of paper face stock, (b) drying the coated web in a drier to remove the water, (c) releasably laminating a continuous web of coated release paper to the dried, adhesive-coated web in the nip of pressure rollers, and (d) winding the resultant laminate on a rewind roll for further processing. The reverse of this is also practiced whereby the water-dispersed pressure-sensitive adhesive is coated to the release paper, the coating dried and then the coated release liner laminated to the face stock and the resultant laminate wound on a rewind roll for further processing.
That further processing generally involves sheeting, slitting or other converting. After that, the laminate is typically printed, cut and collated by a printer to form individual printed sheets. Such sheets may be utilized for any number of uses including name tags, stickers, labels, etc., by simply peeling away the release liner and pressing the adhesive coated side of the face sheet to the desired substrate.
Problems are encountered with both of these methods, however, in the form of wrinkles or curl primarily due to the instability of the resultant laminate because one of the laminae just prior to assembly has lost some of its normal moisture having been exposed to heat in the drier while the other laminae which was not dried has its normal moisture content. This resultant unstable laminate, when exposed to atmospheric conditions relieves the stresses imparted to it by curling or developing wrinkles wherein the release paper detaches itself from the adhesive.
A laminate exhibiting curl or wrinkles is almost impossible to print or further convert and is therefore of little value. One method of overcoming the defects just described is to subject the member of the laminate emerging from the drier to a process which reintroduces sufficient moisture to it to produce a laminate which is stable when exposed to atmospheric conditions. This may be accomplished by spraying moisture on the dried web or putting it through a humidity conditioning section. However, it is somewhat difficult to reintroduce the exact moisture content into the dried web to permit it to be in equilibrium moisture content with the other member of the laminate.